package com.lzhsite.technology.redis.redislockframework;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.StringRedisSerializer;
/**
 * 分布式锁
 * 性能待测试
 * @author lzhcode
 *
 */
public class RedisLock2 {

	  private static Logger logger = LoggerFactory.getLogger(RedisLock.class);

	    private RedisTemplate redisTemplate;

	    private static final int DEFAULT_ACQUIRY_RESOLUTION_MILLIS = 100;

	    /**
	     * Lock key path.
	     */
	    private String lockKey;

	    /**
	     * 锁超时时间，防止线程在入锁以后，无限的执行等待
	     */
	    private int expireMsecs = 60 * 1000;

	    /**
	     * 锁等待时间，防止线程饥饿
	     */
	    private int timeoutMsecs = 10 * 1000;

	    private volatile boolean locked = false;

	    /**
	     * Detailed constructor with default acquire timeout 10000 msecs and lock expiration of 60000 msecs.
	     *
	     * @param lockKey lock key (ex. account:1, ...)
	     */
	    public RedisLock2(RedisTemplate redisTemplate, String lockKey) {
	        this.redisTemplate = redisTemplate;
	        this.lockKey = lockKey + "_lock";
	    }

	    /**
	     * Detailed constructor with default lock expiration of 60000 msecs.
	     *
	     */
	    public RedisLock2(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs) {
	        this(redisTemplate, lockKey);
	        this.timeoutMsecs = timeoutMsecs;
	    }

	    /**
	     * Detailed constructor.
	     *
	     */
	    public RedisLock2(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs, int expireMsecs) {
	        this(redisTemplate, lockKey, timeoutMsecs);
	        this.expireMsecs = expireMsecs;
	    }

	    /**
	     * @return lock key
	     */
	    public String getLockKey() {
	        return lockKey;
	    }

	    private String get(final String key) {
	        Object obj = null;
	        try {
	            obj = redisTemplate.execute(new RedisCallback<Object>() {
	                @Override
	                public Object doInRedis(RedisConnection connection) throws DataAccessException {
	                    StringRedisSerializer serializer = new StringRedisSerializer();
	                    byte[] data = connection.get(serializer.serialize(key));
	                    connection.close();
	                    if (data == null) {
	                        return null;
	                    }
	                    return serializer.deserialize(data);
	                }
	            });
	        } catch (Exception e) {
	            logger.error("get redis error, key : {}", key);
	        }
	        return obj != null ? obj.toString() : null;
	    }

	    private boolean setNX(final String key, final String value) {
	        Object obj = null;
	        try {
	            obj = redisTemplate.execute(new RedisCallback<Object>() {
	                @Override
	                public Object doInRedis(RedisConnection connection) throws DataAccessException {
	                    StringRedisSerializer serializer = new StringRedisSerializer();
	                    Boolean success = connection.setNX(serializer.serialize(key), serializer.serialize(value));
	                    connection.close();
	                    return success;
	                }
	            });
	        } catch (Exception e) {
	            logger.error("setNX redis error, key : {}", key);
	        }
	        return obj != null ? (Boolean) obj : false;
	    }

	    private String getSet(final String key, final String value) {
	        Object obj = null;
	        try {
	            obj = redisTemplate.execute(new RedisCallback<Object>() {
	                @Override
	                public Object doInRedis(RedisConnection connection) throws DataAccessException {
	                    StringRedisSerializer serializer = new StringRedisSerializer();
	                    byte[] ret = connection.getSet(serializer.serialize(key), serializer.serialize(value));
	                    connection.close();
	                    return serializer.deserialize(ret);
	                }
	            });
	        } catch (Exception e) {
	            logger.error("setNX redis error, key : {}", key);
	        }
	        return obj != null ? (String) obj : null;
	    }

	    /**
	     * 获得 lock.
	     * 实现思路: 主要是使用了redis 的setnx命令,缓存了锁.
	     * reids缓存的key是锁的key,所有的共享, value是锁的到期时间(注意:这里把过期时间放在value了,没有时间上设置其超时时间)
	     * 执行过程:
	     * 1.通过setnx尝试设置某个key的值,成功(当前没有这个锁)则返回,成功获得锁
	     * 2.锁已经存在则获取锁的到期时间,和当前时间比较,超时的话,则设置新的值
	     *
	     * @return true if lock is acquired, false acquire timeouted
	     * @throws InterruptedException in case of thread interruption
	     */
	    public synchronized boolean lock() throws InterruptedException {
	        int timeout = timeoutMsecs;
	        while (timeout >= 0) {
	            long expires = System.currentTimeMillis() + expireMsecs + 1;
	            String expiresStr = String.valueOf(expires); //锁到期时间
	            if (this.setNX(lockKey, expiresStr)) {
	                // lock acquired
	                locked = true;
	                return true;
	            }

	            String currentValueStr = this.get(lockKey); //redis里的时间
	            if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
	                //判断是否为空，不为空的情况下，如果被其他线程设置了值，则第二个条件判断是过不去的
	                // lock is expired

	                String oldValueStr = this.getSet(lockKey, expiresStr);
	                //获取上一个锁到期时间，并设置现在的锁到期时间，
	                //只有一个线程才能获取上一个线上的设置时间，因为jedis.getSet是同步的
	                if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
	                    //防止误删（覆盖，因为key是相同的）了他人的锁——这里达不到效果，这里值会被覆盖，但是因为什么相差了很少的时间，所以可以接受

	                    //[分布式的情况下]:如过这个时候，多个线程恰好都到了这里，但是只有一个线程的设置值和当前值相同，他才有权利获取锁
	                    // lock acquired
	                    locked = true;
	                    return true;
	                }
	            }
	            timeout -= DEFAULT_ACQUIRY_RESOLUTION_MILLIS;

	            /*
	                延迟100 毫秒,  这里使用随机时间可能会好一点,可以防止饥饿进程的出现,即,当同时到达多个进程,
	                只会有一个进程获得锁,其他的都用同样的频率进行尝试,后面有来了一些进行,也以同样的频率申请锁,这将可能导致前面来的锁得不到满足.
	                使用随机的等待时间可以一定程度上保证公平性
	             */
	            Thread.sleep(DEFAULT_ACQUIRY_RESOLUTION_MILLIS);

	        }
	        return false;
	    }


	    /**
	     * Acqurired lock release.
	     */
	    public synchronized void unlock() {
	        if (locked) {
	            redisTemplate.delete(lockKey);
	            locked = false;
	        }
	    }

}
